Polycarbonate-siloxane copolymers

ABSTRACT

A polycarbonate is provided which contains residues of a dihydric phenol, at least one comonomer of a siloxane functional bisphenol, optionally, a branching agent and optionally, a flame retardant. Further embodiments of the present invention includes a method for producing a flame retardant polycarbonate.

BACKGROUND OF THE INVENTION

[0001] This invention belongs to the field of polycarbonates. Inparticular, it relates to polycarbonate-siloxane copolymers.

[0002] Historically, flame retardance systems for polycarbonate utilizelow levels of additives to provide flame poisoning and anti-dripbehavior. The most commonly employed flame poisons are organic brominecompounds, organophosphates, and salts of sulfonic acids. Dripinhibition is effectively provided by poly(tetrafluoroethylene), PTFE.Unfortunately, organic bromine derivatives are prohibited as eco-labeladditives; organophosphates are unsuitable because at the levelsrequired for their effectiveness, they plasticize polycarbonate reducingboth continuous use temperature and impact strength to impracticallevels; and PTFE is unsuitable due to its crystallinity and refractiveindex mismatch with polycarbonate that preclude its use in transparentproducts. Salts of sulfonic acids provide flame retardant properties topolycarbonate in thick samples (3.2 millimeters) for normal or low flowpolycarbonate, but for high flow products, they are ineffective withoutdrip inhibitors.

[0003] Due to the restraints of flame retardant additives, it would beadvantageous to have a polycarbonate with a minimum amount of flameretardant additives that also maintains transparent properties. Thus, aneed exists for polycarbonates having flame retardancy and high flowwhile maintaining transparency.

SUMMARY OF THE INVENTION

[0004] The present invention provides a polycarbonate comprisingresidues of;

[0005] (a) at least one dihydric phenol; and

[0006] (b) at least one comonomer comprising a siloxane functionalbis-phenol of the formula

[0007] wherein R is an alkyl group, cycloalkyl group, aryl group,fluoroalkyl group, or combinations thereof and n is in a range between 0and 20;

[0008] (c) optionally, a branching agent; and

[0009] (d) optionally, a flame retardant.

[0010] The further embodiment of the present invention includes a methodfor producing a flame retardant polycarbonate comprising providing:

[0011] (a) at least one dihydric phenol; and

[0012] (b) at least one comonomer comprising a siloxane functionalbis-phenol of the formula

[0013] wherein R is an alkyl group, cycloalkyl group, aryl group,fluoroalkyl group, or combinations thereof and n is in a range between 0and 20;

[0014] (c) optionally, a branching agent; and

[0015] (d) optionally, a flame retardant

[0016] wherein the resulting polycarbonate is transparent.

DETAILED DESCRIPTION OF THE INVENTION

[0017] In this specification and in the claims which follow, referencewill be made to a number of terms which shall be defined to have thefollowing meanings.

[0018] The singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise.

[0019] “Optional” or “optionally” means that the subsequently describedevent or circumstances may or may not occur, and that descriptionincludes instances where the event or circumstance occurs and instanceswhere it does not.

[0020] “BPA” is herein defined as Bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

[0021] Unless otherwise stated, “weight percent” in reference to thecomposition of a polycarbonate in this specification is based upon 100weight percent of the repeating units of the polycarbonate. Forinstance, “a polycarbonate comprising 90 weight percent of BPA” refersto a polycarbonate in which 90 weight percent of the repeating units areresidues derived from Bisphenol A or its corresponding derivative(s).Corresponding derivatives include, but are not limited to, correspondingoligomers of the diphenols; corresponding esters of the diphenol andtheir oligomers; and the corresponding chloroformates of the diphenoland their oligomers.

[0022] The present invention provides a polycarbonate comprisingresidues of;

[0023] (a) a dihydric phenol; and

[0024] (b) at least one comonomer comprising a siloxane functionalbisphenol of the formula

[0025] wherein R is an alkyl group, cycloalkyl group, aryl group,fluoroalkyl group, or combinations thereof and n is in a range between 0and 20;

[0026] (c) optionally, a branching agent; and

[0027] (d) optionally, a flame retardant. Typically, R is a methyl groupor a phenyl group

[0028] The utilization of the above monomers provides a usefulcombination of flame retardancy and high flow to the polycarbonatecompositions as well as transparency. As used hereinafter, the term“flame retardant” means reduced or eliminated in tendency to ignite whenexposed to a low-energy flame. As used hereinafter, the term“transparent” means a maximum percent haze of 15 and a minimum percenttransmission of 75. As used hereinafter, “high flow” means a melt flowindex no less than about 15 grams per 10 minutes at 300° C. and 1.2kilograms.

[0029] The siloxane functional bisphenol is typically utilized inproportions in a range between about 1 mole percent and about 10 molepercent relative to the amount of the dihydric phenol, and moretypically, in a range between about 1 mole percent and about 5 molepercent of the dihydric phenol. In this regard, the use of the term“residue” denotes that portion of the molecule or moiety which remainsafter the polycondensation reaction has taken place.

[0030] The dihydric phenol typically used in the present invention is2,2-bis(4-hydroxyphenyl) propane (BPA). Optionally, the polycarbonatemay be further comprised of other dihydric phenol compound residues inan amount up to about 10 to 50 weight percent of the repeating units inthe polycarbonate, thereby replacing the Bisphenol A, of the presentinvention in the total amount of dihydric phenol compounds utilized.Examples of such compounds include the following:

[0031] resorcinol

[0032] 4-bromoresorcinol

[0033] hydroquinone

[0034] 4,4′-dihydroxybiphenyl ether

[0035] 4,4-thiodiphenol

[0036] 1,6-dihydroxynaphthalene

[0037] 2,6-dihydroxynaphthalene

[0038] bis(4-hydroxyphenyl)methane

[0039] bis(4-hydroxyphenyl)diphenylmethane

[0040] bis(4-hydroxyphenyl)-1-naphthylmethane

[0041] 1,1-bis(4-hydroxyphenyl)ethane

[0042] 1,1-bis(4-hydroxyphenyl)propane

[0043] 1,2-bis(4-hydroxyphenyl)ethane

[0044] 1,1-bis(4-hydroxyphenyl)-1-phenylethane

[0045] 1,1-bis(3-methyl-4-hydroxyphenyl)-1-phenylethane

[0046] 2-(4-hydroxyphenyl)-2-)3-hydroxyphenyl)propane

[0047] 2,2-bis(4-hydroxyphenyl)butane

[0048] 1,1-bis(4-hydroxyphenyl)isobutane

[0049] 1,1-bis(4-hydroxyphenyl)decane

[0050] 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane

[0051] 1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane

[0052] 1,1-bis(4-hydroxyphenyl)cyclohexane

[0053] 1,1-bis(4-hydroxyphenyl)cyclododecane

[0054] 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane

[0055] trans-2,3-bis(4-hydroxyphenyl)-2-butene

[0056] 4,4-dihydroxy-3,3-dichlorodiphenyl ether

[0057] 4,4-dihydroxy-2,5-dihydroxy diphenyl ether

[0058] 2,2-bis(4-hydroxyphenyl)adamantane

[0059] α,α′-bis(4-hydroxyphenyl)toluene

[0060] bis(4-hydroxyphenyl)acetonitrile

[0061] 2,2-bis(3-methyl-4-hydroxyphenyl)propane

[0062] 2,2-bis(3-ethyl-4-hydroxyphenyl)propane

[0063] 2,2-bis(3-n-propyl-4-hydroxyphenyl)propane

[0064] 2,2-bis(3-isopropyl-4-hydroxyphenyl)propane

[0065] 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane

[0066] 2,2-bis(3-t-butyl-4-hydroxyphenyl)propane

[0067] 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane

[0068] 2,2-bis(3-allyl-4-hydroxyphenyl)propane

[0069] 2,2-bis(3-methoxy-4-hydroxyphenyl)propane

[0070]2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane

[0071] 2,2-bis(2,3,5,6-tetramethyl-4-hydroxyphenyl)propane

[0072] 2,2-bis(3-5-dichloro-4-hydroxyphenyl)propane

[0073] 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane

[0074] 2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane

[0075] α,α-bis(4-hydroxyphenyl)toluene

[0076] α,α,α′,α′-Tetramethyl-α,α′-bis(4-hydroxyphenyl)-p-xylene

[0077] 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene

[0078] 1,1-dibromo-2,2-bis(4-hydroxyphenyl)ethylene

[0079] 1,1-dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene

[0080] 4,4-dihydroxybenzophenone

[0081] 3,3-bis(4-hydroxyphenyl)-2-butanone

[0082] 1,6-bis(4-hydroxyphenyl)-1,6-hexanedione

[0083] ethylene glycol bis(4-hydroxyphenyl)ether

[0084] bis(4-hydroxyphenyl)ether

[0085] bis(4-hydroxyphenyl)sulfide

[0086] bis(4-hydroxyphenyl)sulfoxide

[0087] bis(4-hydroxyphenyl)sulfone

[0088] bis(3,5-dimethyl-4-hydroxyphenyl)sulfone

[0089] 9,9-bis(4-hydroxyphenyl)fluorene

[0090]2,7-dihydroxypyrene

[0091]6,6′-dihydroxy-3,3,3′,3′-tetramethylspiro(bis)indane(“spirobiindaneBisphenol”)

[0092] 3,3-bis(4-hydroxyphenyl)phthalide

[0093] 2,6-dihydroxydibenzo-p-dioxin

[0094] 2,6-dihydroxythianthrene

[0095] 2,7-dihydroxyphenoxathiin

[0096] 2,7-dihydroxy-9,10-dimethylphenazine

[0097] 3,6-dihydroxydibenzofuran

[0098] 3,6-dihydroxydibenzothiophene

[0099] 2,7-dihydroxycarbazole.

[0100] The dihydric phenols (which are other than BPA) may be used aloneor as mixtures of two or more dihydric phenols. Further illustrativeexamples of dihydric phenols include the dihydroxy-substituted aromatichydrocarbons disclosed in U.S. Pat. No. 4,217,438.

[0101] In the polycarbonates of the present invention branching agentsmay optionally be used and may comprise polyfunctional organic compoundscontaining at least three functional groups which may be hydroxyl,carboxyl, carboxylic anhydride, haloformyl and mixtures comprising atleast one of the foregoing. Specific examples include trimellitic acid,trimellitic anhydride, trimellitic trichloride, tris-hydroxyphenylethane (THPE), isatin-bis-phenol, tris-phenol TC(1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA(4(4(1,1-bis(p-hydroxyphenyl)-ethyl) alpha,alpha-dimethylbenzyl)phenol), 4-chloroformyl phthalic anhydride, trimesic acid andbenzophenone tetracarboxylic acid, and the like. Preferably, thebranching agent is tris-hydroxyphenylethane (THPE). The branching agentsmay be added at a level in a range between about 0 mole percent andabout 0.5 mole percent, and preferably in a range between about 0.1 molepercent and about 0.5 mole percent relative to the amount of dihydricphenol.

[0102] In the polycarbonates of the present invention an endcappingagent may optionally be used. Suitable endcapping agents includemonovalent aromatic hydroxy compounds, haloformate derivatives ofmonovalent aromatic hydroxy compounds, monovalent carboxylic acids,halide derivatives of monovalent carboxylic acids, and mixtures thereof.Examples of endcapping agents include, but are not limited to, phenol;p-tert-butylphenol; p-cumylphenol; p-cumylphenolcarbonate; undecanoicacid; lauric acid; stearic acid; phenyl chloroformate; t-butyl phenylchloroformate; p-cumyl chloroformate; chroman chloroformate; octylphenyl; nonyl phenyl chloroformate; or a mixture thereof. If present,the endcapping agent is present in amounts in a range between about 1mole percent and about 6 mole percent, typically in a range betweenabout 2 mole percent and about 5 mole percent, even more typically in arange between about 2 mole percent and about 4 mole percent relative tothe dihydric phenol.

[0103] The method of preparation of polycarbonates by interfacialpolymerization are well know; see for example the details provided inthe U.S. Pat. Nos. 3,028,365; 3,334,154; 3,275,601; 3,915,926;3,030,331; 3,169,121; and 4,188,314.

[0104] Although the reaction conditions of the preparative processes mayvary, several of the preferred processes typically involve dissolving ordispersing the dihydric phenol reactant in aqueous caustic soda orpotash, adding the resulting mixture with the siloxane to a suitablewater immiscible solvent medium and contacting the reactants with thecarbonate precursor, such as phosgene, in the presence of a suitablecatalyst such as triethylamine and under controlled pH conditions, e.g.,8-10. The most commonly used water immiscible solvents include methylenechloride, 1,2-dichloroethane, chlorobenzene, toluene, and the like.

[0105] A catalyst may be employed to accelerate the rate ofpolymerization of the dihydroxy phenol reactant with the carbonateprecursor. Representative catalysts include, but are not limited totertiary amines such as triethylamine, quartemary phosphonium compounds,quaternary ammonium compounds, and the like. The preferred process forpreparing resins of the present invention comprises the phosgenationreaction. The temperature at which the phosgenation reaction proceedsmay vary from below 0° C. to about 100° C. The phosgenation reactionpreferably proceeds at temperature of from room temperatures (25° C. to50° C.). Since the reaction is exothermic, the rate of phosgene additionmay be used to control the reaction temperature. The amount of phosgenerequired will generally depend upon the amount of the dihydric phenolreactant and the amount of siloxane also present.

[0106] Alternatively, the polycarbonate copolymer may be prepared byco-reacting in a molten state, the diphenolic monomers and a diarylcarbonate ester, such as diphenyl carbonate, in the presence of atransesterification catalyst in a Banbury mixer, twin screw extruder, orthe like to form a uniform dispersion. Volatile monohydric phenol isremoved from the molten reactants by distillation and the polymer isisolated as a molten residue.

[0107] Optionally, the polycarbonate may further includeacrylonitrile-butadiene-styrene (ABS) copolymers, which are typicallygrafts of styrene or substituted styrenes and acrylonitrile orsubstituted acrylonitriles on a previously formed diene polymer backbone(e.g., polybutadiene or polyisoprene). Theacrylonitrile-butadiene-styrene copolymer may typically be present in arange between about 3 weight percent and 30 weight percent, moretypically in a range between about 3 weight percent and about 15 weightpercent, and most typically in a range between about 3 weight percentand about 8 weight percent of the total composition.

[0108] Styrene and substituted styrenes are vinyl aromatic monomershaving one or more alkyl, alkoxyl, hydroxyl or halo substituent groupsattached to the aromatic ring, including, e.g., α-methyl styrene,p-methyl styrene, vinyl toluene, vinyl xylene, trimethyl styrene, butylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, p-hydroxystyrene,methoxystyrene and vinyl-substituted condensed aromatic ring structures,such as, e.g., vinyl naphthalene, vinyl anthracene, as well as mixturesof vinyl aromatic monomers.

[0109] Acrylonitriles are examples of “monoethylenically unsaturatednitrile monomers” which are acyclic compounds that includes a singlenitrile group and a single site of ethylenic unsaturation per molecule.Other monoethylenically unsaturated nitrile monomers include, forexample, methacrylonitrile and α-chloro acrylonitrile.

[0110] Suitable acrylonitrile-butadiene-styrene copolymers may beproduced by any method known in the art. In a preferred embodiment ofthe present invention, a suitable ABS is a high rubber graftacrylonitrile-butadiene-styrene copolymer produced in a process whichincludes an emulsion polymerization step. The phrase “high rubber graft”refers generally to graft copolymer resins wherein at least about 30weight percent, preferably at least about 45 weight percent of the rigidpolymeric phase is chemically bound or grafted to the elastomericsubstrate phase. Suitable ABS-type high rubber graft copolymers arecommercially available from, for example, GE Plastics, Inc. under thetrademark BLENDEX and include grades 131, 336, 338, 360, and 415. Inanother preferred embodiment of the present invention, a suitable ABS isone produced in a process which includes a mass polymerization step,so-called bulk ABS.

[0111] In addition, the present invention provides shaped, formed, ormolded articles comprising the polycarbonates of the present invention.

[0112] Additives may also be added to the polycarbonate product as longas they do not adversely affect the properties of the product. Theseadditives include a wide range of substances that are conventionallyadded to the polycarbonates for a variety of purposes. Specific examplesinclude anti-drip agents, heat stabilizers, epoxy compounds, ultravioletabsorbers, mold release agents, colorants, antistatic agents, slippingagents, anti-blocking agents, lubricants, antifogging agents, naturaloils, synthetic oils, waxes, organic fillers, inorganic fillers and anyother commonly known class of additives.

[0113] Flame retardants may optionally be used in the present inventionin a range between about 2 weight % and about 8 weight % relative to theamount of the total composition. Examples of flame retardants in thepresent invention include phosphoramides. In one embodiment, thephosphoramide comprises a compound of the formula (II):

[0114] wherein each Q¹ is independently oxygen or sulfur; and each ofA³⁻⁶ is independently an alkyloxy, alkylthio, aryloxy, or arylthioresidue, or an aryloxy or arylthio residue containing at least one alkylor halogen substitution, or mixture thereof; or an amine residue. In apreferred embodiment each Q¹ is oxygen, and each A³⁻⁶ is an aryloxymoiety with at least one aryloxy moiety having at least one substituenton an aromatic ring ortho to the oxygen linkage. In a more preferredembodiment each Q¹ is oxygen, and each A³⁻⁶ moiety is independently anaryloxy moiety with at least one substituent on each aromatic ring orthoto the oxygen linkage, optionally further substituted. In a still morepreferred embodiment of the present invention, each Q¹ is oxygen, andeach A³⁻⁶ moiety is independently an aryloxy moiety with at least twosubstituents on each aromatic ring ortho to the oxygen linkage, as forexample a 2,6-disubstituted phenoxy moiety, optionally furthersubstituted. Preferred substituents are C₁₋₈ straight-chain or branchedalkyl, or halogen. In an especially preferred embodiment of the presentinvention, each Q¹ is oxygen, and each A³⁻⁶ moiety is independentlyphenoxy, 2,6-dimethylphenoxy, 2,3,6-trimethylphenoxy, or2,4,6-trimethylphenoxy. In a more especially preferred embodiment of theinvention, each Q¹ is oxygen, and all A³⁻⁶ moieties are phenoxy,2,6-dimethylphenoxy, 2,3,6-trimethylphenoxy, or 2,4,6-trimethylphenoxy.These phosphoramides are piperazine-type phosphoramides.

[0115] Other flame retardants which may be used in the present inventioninclude, for example, triphenyl phosphate (TPP), resorcinol diphosphate(RDP) and bisphenol-a-disphophate (BPA-DP); and mixtures thereof.

[0116] Such copolymers or resins described herein can be used forinstance as: housings for computer equipment (monitors, CPUs, printers),electrical connectors, components or housings for telecomm equipment(cell phones, handheld devices), and other applications that couldrequire transparency and flame retardance.

[0117] In order that those skilled in the art will be better able topractice the present invention, the following examples are given by wayof illustration and not by way of limitation.

EXAMPLES

[0118] A 500 milliliter (mL) 5-neck indented wall flask was charged with21.66 grams (g)(0.095 mol) of BPA, 0.743 g (0.004 mol) of p-cumylphenol,2.311 g (0.005 mol) of1,3-bis-3-(3-methoxy-4-hydroxy)phenylpropyl-1,1,3,3-tetramethyldisiloxane,140 microliters of triethylamine (catalyst), 90 mL of water and 115 mLof methylene chloride. The flask was fitted with a gas inlet tube,condenser, pH probe, caustic inlet tube, and a stirring shaft connectedto a motor. The mixture was stirred vigorously while phosgene wasintroduced at a rate of 0.6 g/minute. The pH was maintained at about10.5 during the phosgene addition by metered addition of 50% sodiumhydroxide (NaOH). When a total of 12.4 g (0.125 mol) of phosgene hadbeen added, gas flow was discontinued and excess phosgene was swept outby means of a nitrogen flow. When no more phosgene or chloroformateswere detected in the reaction mixture as judged by a negative test withphosgene indicator paper, the contents of the vessel were transferred toa separatory funnel. The organic phase was separated and washed with 2volumes of 10% hydrochloric acid (HCl) and 3-5 volumes of water (untilthe pH of the washes were neutral). The polymer was isolated byprecipitation into boiling water. This afforded about 23 g of copolymerpowder which was characterized by ¹H and ²⁹Si nuclear magnetic resonancespectroscopy (NMR). The glass transition temperature (Tg) of the polymerwas 129.5° C. Molecular weights (relative to polystyrene) were measuredas: Molecular weight=45,110; Molecular number=15,456.

[0119] The copolymer powders prepared via the synthesis were firstcompounded on a 16 millimeter (mm) twin screw extruder with a maximumtemperature of 265° C. Flame bars were injection molded at a temperatureof 271° C. Table 1 shows the UL94 flame performance using the verticalburning (V-0/V-1) procedure. Total burn times (t₁+t₂) for the 5 barsplus the UL rating are listed in Table 1. Comparative sample 1 (Comp. 1)is pure polycarbonate of a similar melt flow.

[0120] The term “UL94” when used in conjunction with “flame retardant”means that a described polycarbonate composition can satisfy the UL94requirements for V-0 flammability, as described in the “Flammability ofPlastic Materials Bulletin” of Jan. 24, 1980. In this test, a 5 inch by½ inch by {fraction (1/16)} inch polycarbonate test bar containing anamount of a flame retardant additive is suspended vertically over a ¾inch Bunsen Burner flame. A material meets requirements for a UL94 V0rating when a test bar satisfies the following 5 tests: (1) a test barof the material does not burn with flaming combustion for more than 10seconds after application of a test flame, (2) no set of five test barsexhibits a total flaming combustion time exceeding 50 seconds for 10flame applications, (3) no test bar of the material burns with flamingor glowing combustion up to the holding clamp, (4) no test bar dripsflaming particles that ignite dry absorbent surgical cotton located 12inches (305 millimeters) below the bar, and (5) no test bar exhibitsglowing combustion that persists for more than 30 seconds after twiceapplying and removing the test flame.

[0121] Also included in Table 1 are MFI data (Melt Flow Index), percenttransmission of light, and percent haze. The MFI data was measured at300° C. with a 1.2 kilogram weight. The resin was allowed to melt for 4minutes before testing was begun. Transmission and haze measurementswere performed on 3.2 mm thick injection molded flame bars. TABLE 1Comp. R Phenyl Phenyl Phenyl Methyl Methyl 1 Branch — THPE Si-based THPE— — Total FOT 13 12 13.3 17 20 49 (sec) Total Drips 0 0 0 0 0 5 RatingV-0 V-0 V-0 V-0 V-0 V-2 % Haze 11.1 14 — 9.5 9.0 4.85 % 84.5 81.2 80.578.9 86.1 Transmission MFI (g/ 33.4 21.9 28.7 24.5 10 min)

[0122] The siloxane functional monomer in these copolymers wasincorporated at a level of 5 mole % relative to the BPA. If a branchingagent was used, it was added at a level of 0.25 mole % relative to theBPA.

[0123] All of the copolymers showed a significant improvement in flameretardancy compared to pure polycarbonate (Comp. 1). In each case thetotal flame out time of the 5 bars was reduced by at least about 60%.Also, dripping was eliminated. At the same time, the percent haze andpercent transmission were still useful for applications requiringtransparency. Finally, the flow of all the copolymers was excellentmaking them useful for thin wall applications.

Example 2

[0124] Acrylonitrile-butadiene-styrene was a product called AT-07obtained from Mitsui Toatsu. The blends of the polycarbonate-siloxanecopolymers and polycarbonatelacrylonitrile-butadiene-styrene wereprepared by compounding on a 20 millimeter (mm) twin screw extruder witha maximum temperature of 274° C. Flame bars were injection molded at atemperature of 290° C.

[0125] In Table 2, different types of polycarbonate-siloxane copolymerswere added to a polycarbonate/acrylonitrile-butadiene-styreneformulation that contained a small amount of a phosphate flameretardant. Table 2 is the percentages of the compounds in theformulations and Table 3 is the results from the UL94 flame performancefor 1.6 mm bars. The amount of phosphate was not enough to provide fullflame retardancy by itself. X4PiP is tetraxylylpiperazinediphosphoramide; salt is potassium perfluorobutane sulfonate; PITFE isthe anti-drip agent polytetrafluoroethylene; and samples 1, 2, 3, and 4were made with tetramethyldisiloxane as the siloxane comonomer. TABLE 2Sample 1 Sample 2 Sample 3 Comp. 1 Sample 4 PC 74.4 55.8 74.3 74.4 —X4PiP 2 2 2 2 — ABS 4.5 4.5 4.5 4.5 4.5 PTFE 0.5 0.5 0.5 0.5 0.5 PC-Si18.6 37.2 18.6 18.6 94.9 Copolymer Salt — — 0.1 — 0.1

[0126] TABLE 3 Sample 1 Sample 2 Sample 3 Comp. 1 Sample 4 Average 4.175.7 7.93 53.47 12.84 FOT per bar (sec) Drip 0 0 0 0 0

[0127] As can be seen in samples 1 and 2, the inclusion of the shortchain copolymer (PC+tetramethyldisiloxane) provided excellent flameretardancy. However, with a longer chain copolymer (repeat unit oftetramethyldisiloxane comonomer=10), the performance was no longer V-0(comparative sample 1). Also, the PC-siloxane copolymer could optionallyalso be used with other FR agents in PC/ABS blends including sulfonatesalts (sample 3). Finally, the use of the PC-siloxane copolymer withoutthe phosphate provided V-1 behavior (sample 4).

[0128] While typical embodiments have been set forth for the purpose ofillustration, the foregoing descriptions should not be deemed to be alimitation on the scope of the invention. Accordingly, variousmodifications, adaptations, and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the presentinvention.

What is claimed is:
 1. A polycarbonate comprising residues of; (a) atleast one dihydric phenol; and (b) at least one comonomer comprising asiloxane functional bis-phenol of the formula

wherein R is an alkyl group, cycloalkyl group, aryl group, fluoroalkylgroup, or combinations thereof and n is in a range between 0 and 20; (c)optionally, a branching agent; and (d) optionally, a flame retardant. 2.The polycarbonate of claim 1, wherein the dihydric phenol is2,2-bis(4-hydroxyphenyl)propane.
 3. The polycarbonate of claim 1,wherein the siloxane functional bis-phenol is present in a range betweenabout 1 mole percent and about 10 mole percent relative to the amount ofthe dihydric phenol.
 4. The polycarbonate of claim 1, wherein thesiloxane functional bis-phenol is present in a range between about 1mole percent and about 5 mole percent relative to the amount of dihydricphenol.
 5. The polycarbonate of claim 1, wherein R is a methyl group. 6.The polycarbonate of claim 1, wherein R is a phenyl group.
 7. Thepolycarbonate of claim 1, wherein the branching agent comprisestris-hydroxyphenylethane.
 8. The polycarbonate of claim 1, wherein thebranching agent is present in a range between about 0 mole percent andabout 0.5 mole percent relative to the amount of the dihydric phenol. 9.The polycarbonate of claim 8, wherein the branching agent is present ina range between about 0.1 mole percent about 0.5 mole percent relativeto the amount of the dihydric phenol.
 10. The polycarbonate of claim 1,further comprising acrylonitrile-butadiene-styrene.
 11. Thepolycarbonate of claim 10, wherein the acrylonitrile-butadiene-styreneis present in a range between about 3 weight percent and about 30 weightpercent relative to the amount of the total composition.
 12. Thepolycarbonate of claim 11, wherein the acrylonitrile-butadiene-styreneis present in a range between about 3 weight percent and about 15 weightpercent relative to the amount of the total composition.
 13. Thepolycarbonate of claim 12, wherein the acrylonitrile-butadiene-styreneis present in a range between about 3 weight percent and about 8 weightpercent relative to the amount of the total composition.
 14. Thepolycarbonate of claim 1, wherein the flame retardant is present in arange between about 2 weight percent and about 8 weight percent relativeto the amount of the total composition.
 15. The polycarbonate of claim1, wherein the flame retardant comprises tetraxylxylpiperazinediphosphoramide.
 16. The polycarbonate of claim 1, further comprising ananti-drip agent.
 17. The polycarbonate of claim 16, wherein theanti-drip agent comprises polytetrafluoroethylene.
 18. The polycarbonateof claim 1, wherein the polycarbonate is transparent.
 19. An articlecomprising the polycarbonate of claim
 1. 20. A polycarbonate comprisingresidues of; (a) 2,2-bis(4-hydroxyphenyl)propane; and (b) at least onecomonomer comprising a siloxane functional bis-phenol of the formula

wherein R is a methyl group or phenyl group and n is in a range between0 and 20; and (c) a branching agent comprising tris-hydroxyphenylethanewherein the polycarbonate is transparent.
 21. An article comprising thepolycarbonate of claim
 20. 22. A method for producing a flame retardantpolycarbonate comprising providing: (a) at least one dihydric phenol;and (b) at least one comonomer comprising a siloxane functionalbis-phenol of the formula

wherein R is an alkyl group, cycloalkyl group, aryl group, fluoroalkylgroup, or combinations thereof and n is in a range between 0 and 20; (c)optionally, a branching agent; and (d) optionally, a flame retardantwherein the resulting polycarbonate is transparent.
 23. The method ofclaim 22, wherein the dihydric phenol is2,2-bis(4-hydroxyphenyl)propane.
 24. The method of claim 22, wherein thesiloxane functional bis-phenol is present in a range between about 1mole percent and about 10 mole percent relative to the amount of thedihydric phenol.
 25. The method of claim 22, wherein the siloxanefunctional bis-phenol is present in a range between about 1 mole percentand about 5 mole percent relative to the amount of dihydric phenol. 26.The method of claim 22, wherein R is a methyl group.
 27. The method ofclaim 22, wherein R is a phenyl group.
 28. The method of claim 22,wherein the branching agent comprises tris-hydroxyphenylethane.
 29. Themethod of claim 22, wherein the branching agent is present in a rangebetween about 0 mole percent and about 0.5 mole percent relative to theamount of the dihydric phenol.
 30. The method of claim 29, wherein thebranching agent is present in a range between about 0.1 mole percentabout 0.5 mole percent relative to the amount of the dihydric phenol.31. The method of claim 22, further comprisingacrylonitrile-butadiene-styrene.
 32. The method of claim 31, wherein theacrylonitrile-butadiene-styrene is present in a range between about 3and about 30 relative to the amount of the total composition.
 33. Themethod of claim 32, wherein the acrylonitrile-butadiene-styrene ispresent in a range between about 3 and about 15 relative to the amountof the total composition.
 34. The method of claim 33, wherein theacrylonitrile-butadiene-styrene is present in a range between about 3and about 8 relative to the amount of the total composition.
 35. Themethod of claim 22, wherein the flame retardant is present in a rangebetween about 2 weight percent and about 8 weight percent relative tothe amount of the total composition.
 36. The method of claim 22, whereinthe flame retardant comprises tetraxylxylpiperazine diphosphoramide. 37.The method of claim 22, further comprising an anti-drip agent.
 38. Themethod of claim 37, wherein the anti-drip agent comprisespolytetrafluoroethylene.
 39. The method of claim 22, wherein thepolycarbonate is transparent.
 40. A method for producing a flameretardant polycarbonate comprising providing: (a)2,2-bis(4-hydroxyphenyl)propane; and (b) at least one comonomercomprising a siloxane functional bis-phenol of the formula

wherein R is a methyl group or phenyl group and n is in a range between0 and 20; and (c) a branching agent comprising tris-hydroxyphenylethanewherein the polycarbonate is transparent.